The present invention relates to a method of heating a melt containing an oxidizable substance. More particularly, the present invention relates to such a method in which the fuel is burned in an oxidant by projecting a fuel jet and an underlying oxidant jet over the melt. Even more particularly, the present invention relates to such a method in which the oxidant jet momentum is controlled so that the top surface of the melt is sufficiently undisturbed that the melt situated beneath the top surface does not rise to the top surface to become oxidized.
The prior art has provided burners in which fuel is burned within an oxidant, oxygen enriched air or nearly pure oxygen to produce a projected flame over the melt. In many such burners, the oxidant is supplied by an oxidant jet positioned below a fuel jet so that the oxidant jet is located between the melt and the fuel jet. In an attempt to project the flame, a high momentum is imparted to the underlying oxidant jet. Typically, however, a high temperature region is produced beneath the flame that contains oxygen. In case of an oxidizable melt such as aluminum, the top surface of the oxidizable melt competes with the fuel for the oxygen to produce a top oxidation layer, known in the art as dross. This top oxidation layer insulates the melt from the flame and, as a result, the power being delivered by the flame to the melt decreases. This in turn increases the amount of fuel required to heat the melt a specified amount.
As will be discussed, the present invention provides a melt heating method which acts to inhibit growth of the top oxidation layer and therefore the insulation provided by such top oxidation layer.